The purpose of this study is to identify risk factors for "classic" Kaposi's sarcoma (KS), with emphasis on the role of the cytomegalovirus (CMV) and the family of Human Lymphotrophic Viruses (HTLV). It is clear that immunosuppression - either secondary to HTLV III - infection or to therapy for organ transplant - is of etiologic significance to the occurrence of KS. There is evidence that CMV infection may be an etiologic factor in these cases as well. No analytic epidemiologic studies have been done on background or "classic" KS. We propose to conduct a collaborative population-based, case-control study in the high risk population in south and central Greece to investigate the roles of CMV, HTLV's, and factors related to immunosuppression in this disease. One hundred incident cases will be identified and interviewed for environmental, medical, and occupational exposures. Blood will be obtained and assayed for a variety of antibodies to the CMV, the HTLV's and the Epstein-Barr Virus (EBV) as a comparison for specificity. HLA typing will be performed and immune function assessed. Biopsy material will be tested for hybridization for CMV, EBV and HTLV genomes. Two control groups will be assembled. A "clinic" group of individuals biopsied for probable KS but found to have non-melanoma skin cancer or benign conditions will be interviewed with the same serologic and biopsy assays. A second control group consists of neighbor controls who will be interviewed and bled. By combined serologic, immunologic and interview information, a comprehensive screening for risk factors and evaluation of roles of the CMV and HTLV's should be achieved.